1. Field of the Invention
The present invention relates to an artificial neural circuit apparatus based on a pulse coding such as a stochastic pulse coding (hereinafter, referred to as "SPC") or a noise feedback pulse coding (hereinafter, referred to as "NFPC").
2. Description of the Prior Art
Among the electronic neural circuits disclosed so far, pulse coding neural circuits have received a great deal of attention in recent years because of their analogy with biological neurons and the effectiveness of weight computation. However, the pulse coding approaches require more computation time for the weighted summation than other approaches.
An elementary nerve cell, called a neuron, is the basic building block of a biological neural network.
FIG. 1 shows a schematic diagram of a typical neuron, which consists of three main parts: a plurality of dendrites 1, a neuron body 2, and a axon hillock 3. The dendrites 1 aggregate synaptic input from other neurons. In detail, the dendrites 1 functionate as input portions, respectively, and are connected with other neurons to receive information from the other neurons. The information indicate input currents which are respectively received through the dendrites 1. The input currents received thus are spacio-temporally integrated by capacitance of the neuron body 2, so that an analog signal, particularly an analog voltage, may be produced in the neuron body 2. The analog signal produced thus is encoded in the initial segment of the axon hillock 3 and converted into a pulse sequence (or a pulse train). At this time, the converted pulse train is propagated to an axon which ends in synaptic contacts to dendrites of other neurons. Synapses 4 in one neuron function as central-information processing elements in neural systems, and control a flow of a current to be applied to a membrane connected therewith.
In recent years, an electric neural circuit has been proposed as a novel information processing device possible to perform similar operation to that of a biological neuron, as described above. The conventional electric neural circuit has used an SPC method so as to convert an analog voltage or a binary digital value into a pulse train. However, in the SPC method, there is a problem that a large number of pulses are required for performing the SPC method and a plurality of random pulse generator possible to operate independently with each other is required in order that concise conversion of the analog voltage into the pulse train can be achieved.